1. Field of the Invention
This invention relates to improvements in a piston assembly of an internal combustion engine, by which engine oil consumption is reduced under a high load condition of the engine and under a negative pressure condition in a corresponding combustion chamber of the engine.
2. Description of the Prior Art
It is well known that various compression rings for pistons have been proposed to reduce oil consumption in internal combustion engines.
One of these compression rings is shown in FIG. 8 of the present application and is disclosed, for example, in Japanese Utility Model Provisional Publication No. 59-126158. Another is shown in FIG. 9 of the present application is disclosed, for example, in Japanese Patent Provisional Publication No. 62-251457.
In FIG. 8, compression ring 10 is such arranged so that its opposite end sections partially overlap to each other. One end section of the compression ring 10 has a recess 14 in a corner formed by an outer periphery 11, an upper surface 12 and an end surface 13. The upper surface 12 is on the side of a corresponding combustion chamber. The other end section of the compression ring 10 has a projection 15 which extends over the first end section to lie upon the recess 14 so as to be in tight contact with the surface of the recess 14.
In FIG. 9, compression ring 16 has opposite end surfaces 17. A lower section of each end surface 17 is chamfered by machining to form a chamfered surface, so that the compression ring 16 has a clearance C.sub.4 between opposite upper sections of its end surfaces 17 and a clearance C.sub.5, larger than the clearance C.sub.4, between opposite lower edges of the chamfered surface.
With an engine having the compression ring 10 or 16, when the combustion chamber of the engine is under a high pressure condition such as during a high load engine operation, lubrication oil is blown down by blow-by gas. In case that the combustion chamber of the engine is under a negative pressure condition such as during an engine-brake operation, the lubrication oil is prevented from being sucked into the combustion chamber. Therefore, the oil consumption is suppressed in both cases.
However, difficulties have been encountered in the above-mentioned arrangements, as follows.
In the structure of FIG. 8, since the end sections of the compression ring 10 have to be formed to a complicated shape and the projection 15 is formed in a blade shape, the cost of machining the ring 10 becomes high while degrading the durability of the ring 10.
In the structure of FIG. 9, since the end sections of the compression ring 16 are formed to a complicated shape, the cost of machining the ring becomes high. Furthermore, since lubrication oil tends to stay at the end surfaces 17 of the compression ring 16, the oil blow-down by the blow-by gas is degraded. Therefore, the oil consumption reduction by the ring 16 is degraded.